The present invention relates to aromatic polyformal carbonates and aromatic polyformal carbonate-aromatic polycarbonate block polymers having improved characteristics with respect to processability as compared to conventional aromatic polycarbonates. The aromatic polyformal carbonate polymers of the present invention are characterized by having chemically combined formal dimer units based on the use of bisphenol-formal dimer.
Prior to the present invention, aromatic polycarbonates, generally recognized as high impact thermoplastics, had high glass transition temperatures, for example, exceeding 150.degree. C. which sometimes interfered with their processability. As taught by Barclay U.S. Pat. 3,069,386, aromatic bisphenols used in the production of aromatic polycarbonates can be modified with formal linkages. The resulting polyformal oligomers can be phosgenated to produce thermoplastic materials exhibiting lower softening points. However, the reaction is subject to undesirable side reactions, and the final polyformal carbonate varies considerably due to the wide variation in the molecular weight of the intermediate polyformal oligomer.
As shown in copending application of Allan S. Hay, Ser. No. 889,393 filed Mar. 23, 1978 and assigned to the same assignee as the present invention, a reaction between bisphenol of the formula, EQU HOROH, (1)
where R is a C.sub.(6-30) divalent aromatic radical, methylene halide, base, and an organic solvent, also can result in a mixture of film forming polyformals and cyclopoly formals. The direct phosgenation of such mixture can be complicated by the presence of the cyclopolyformals.